In a W-CDMA (Wideband Code Division Multiple Access) radio communication system, a third generation mobile communication system, an uninterruptible hard handover (HHO) is performed for service switchover, service transmission speed change, spreading code reassignment, etc. The service switchover processing signifies processing to switch over from control signal transmission to packet transmission, for example. Based on the criterion of reference timing CFN (Connection Frame Number), radio base station apparatus (BTS: Base Transceiver Station) and mobile terminal apparatus (UE: User Apparatus) perform the HHO processing under a specified identical CFN. The CFN is a counter with a period of 256 counts in the unit of 10 ms. The BTS and the UE count an identical CFN in synchronization, and simultaneously switch the service at the specified identical CFN. More specifically, in a physical channel (DPCH) between the BTS and the UE, for example, the HHO processing is performed at the time of switching transfer rates from 15 kbps to 240 kbps, or switching channels from “DPDCH+DPCCH”, which is the DPCH channel standardized in Release 99 of the 3GPP, to “HS-DSCH”, which is an HSDPA service standardized in Release 5.
Additionally, in the W-CDMA system, BTS switchover is not hard handover processing because a system that the UE simultaneously communicates with a plurality of BTS [rake reception, or soft handover (SHO)] is adopted when a radio wave condition between UE and BTS becomes bad (in consideration of quality as well as intensity). However, when a service switchover (for example, switching from a channel based on Release 99 to a channel based on Release 5) is made simultaneously with the BTS switchover, the service switchover concerned is hard handover processing. A frequency switchover in the BTS switchover is also hard handover processing. Further, in the patent document 1 illustrated below, there is disclosed an uninterruptible hard handover in the “expelling” control of a maintenance function.
In regard to CFN for designating timing to perform HHO processing, based on either a service switchover request from the UE side or a service switchover request from an upper level of base station control apparatus (RNC: Radio Network Controller) on the network side, a call processing unit in the RNC determines a CFN for specifying HHO timing, so as to notify the BTS and the UE. With this, the BTS and the UE performs HHO processing under the identical CFN.
FIG. 1 is a diagram illustrating an exemplary configuration of the W-CDMA system. The W-CDMA system is constituted of a mobile terminal (UE: User Apparatus), radio base station apparatus (BTS: Base Transceiver Station) and base station control apparatus (RNC: Radio Network Controller). Under the subordination of the base station control apparatus (hereafter referred to as RNC), a plurality of sets of radio base station apparatus (hereafter referred to as BTS) are allocated, although not illustrated in the figure. The BTS performs radio communication with a plurality of mobile terminals (hereafter referred to as UE) located in the BTS area concerned.
Each the UE, the BTS and the RNC includes a call control unit for managing call control, and a processing unit for processing each layer of the protocol in conformity of the OSI (Open System Interconnection) model. As a portion thereof, in FIG. 2, there are illustrated a baseband processing unit (BB unit) in the UE for performing MAC (Media Access Control) processing and physical layer processing (PHY processing) at the UE, a BB unit in the BTS for performing physical layer processing (PHY processing) and transport network layer processing (TNL processing) at the BTS, and a BB unit in the RNC for performing MAC processing and transport network layer processing (TNL processing) at the RNC. In a downlink, the MAC processing and the TNL processing at the RNC perform logical channel (DCCH: Dedicated Control Channel and DTCH: Dedicated Traffic Channel) transmission to the BTS, and the TNL processing and the PHY processing at the BTS perform transport processing of the logical channels, so as to transmit to the UE by mapping each logical channel to a physical channel (DPCH: Dedicated Physical Channel). The PHY processing and the MAC processing at the UE perform the conversion of the physical channel DPCH to the logical channel (DCCH, DTCH).
FIG. 2 is an operating sequence of HHO processing in the W-CDMA system. The call control unit in the RNC generates HHO request information including an HHO command and a CFN for HHO timing (S10), and sends to the BTS the HHO request information destined to the BTS through a C-Plane (Control Plane) (S12). The call control unit in the BTS receives the HHO request information destined to the BTS. Also, the call control unit in the RNC sends to the UE the HHO request information destined to the UE via the BB unit in the BTS (S14, S16). The HHO request information from the RNC to the UE is first transmitted to the BB unit in the BTS, through the logical channel of a U-Plane (User Plane) (S14), and is sent to the UE from the BB unit in the BTS through the physical channel (S16).
The call control unit in the UE performs the HHO processing at the timing of the specified CFN included in the received HHO request information.
On the other hand, the call control unit in the BTS sends the HHO request information received in S12 to the BB unit in the BTS which performs the HHO processing, (S18), and the BB unit in the BTS performs the HHO processing. At this time, when the notification in S18 is delayed due to the congestion of processing in the call control unit of the BTS, the execution of the HHO processing in the BB unit may be delayed from the timing of the specified CFN. FIG. 2 illustrates a case that the HHO processing in the BTS is performed at the timing of the specified CFN+3. In this case, because of the deviation of the HHO processing timing between the BTS and the UE, a missing data is produced in the above deviating period.
In FIG. 2, the deviation of the HHO processing timing between the BTS and the UE due to the processing delay in the call control unit of the BTS is exemplified. Similarly, due to a processing delay in the BB unit of the BTS, there may be cases that deviation of HHO processing timing be produced because of a delay of the HHO processing from the specified CFN in the BB unit of the BTS. Also, due to a processing delay in the BB unit of the BTS, deviation of HHO processing timing may be produced because of a transfer delay of the HHO request information to the UE, and an HHO processing delay from the specified CFN in the UE.
[Patent Document 1]
Japanese Laid-open Patent Publication No. 2004-80698